1. Field of the Invention
The invention relates to a minimally invasive surgery (MIS) technique and devices for performing laminar osteotomy and laminoplasty; with or without visual or image assistance such as cameras used with endoscopy, fluoroscopy, CT, or MRI.
2. Related Art
Spinal stenosis is a condition characterized by a narrowing of the central spinal canal or inter vertebral foramen. Spinal stenosis results in back and leg pain due to the compression of spinal nerves. Severe cases of spinal stenosis require spinal decompressive laminectomy surgery or spinal laminoplasty surgery to enlarge the spinal canal and relieve pressure on the neuronal elements. These neuronal elements consist of the spinal cord, conus medullaris, nerve roots, and all other structures covered by the dura mater (a connective tissue membrane covering the neuronal elements). Pressure on the neuronal elements is relieved by removing or reshaping, in part or completely, structures that are the source of compression, which may include bone or soft tissues (ligaments, joint capsule, and other non-bone structures).
Spinal stenosis is considered primary (congenital) or secondary (acquired). Isolated primary spinal stenosis is very uncommon and involves spinal canal narrowing caused by a congenital abnormality or a disorder in development. Secondary stenosis usually results from degenerative changes.
Decompressive laminectomy is the standard surgical procedure for patients with spinal stenosis, when non-surgical treatments have failed. The surgery is traditionally accomplished via a posterior approach, with the patient prone under general anesthesia. In the posterior approach, after a sterile field is established, a longitudinal incision is made along the midline posteriorly at the level of the stenosis. The incision is carried down to the posterior elements identifying the spinous process, the lamina, and the facet joints. An X-ray or other fluoroscopic image is usually obtained with a radio-opaque marker to ensure that the correct spinal level has been exposed. The musculotendonous attachments to the posterior elements are systematically removed to expose the vertebral anatomy. The facet joints may be partially or completely removed based on the pathology that is present. Removal of a significant part or the entire facet joints will result in spinal instability. In such cases, a spinal fusion is typically required to stabilize the spine.
Another surgical method to create additional room in the spinal canal is called a laminoplasty. In this technique the lamina is divided, spread apart, and a bone graft is to inserted to enlarge the space available for the neuronal elements. Laminoplasty can be performed using unilateral or open door laminoplasty. In unilateral or open door laminoplasty, the lamina of one side of the vertebra is divided completely, while the other side is partially cut to create a hinge. The vertebral posterior element is then rotated about the hinge, and a graft is inserted into the opening, increasing the spinal canal space. Another laminoplasty procedure is called the bilateral or French door laminoplasty in which the spinous process (where the lamina meet in the posterior midline) is divided completely. Each lamina on either side of the posterior midline is then cut half way through, creating two hinges. The separated posterior elements are then opened at the cut spinous process, and a graft is inserted into the opening, again increasing the opening of the spinal canal.
Traditionally, laminectomies and laminoplasties are open surgical procedures resulting in extensive recovery times for patients and increased costs and risks of complications. Thus, there has been a demand for MIS techniques and tools to perform laminectomies and laminoplasties. Further, MIS techniques are becoming more widespread in the surgical subspecialties. Standard open surgical procedures are being modified to become less invasive, with the goal of decreased recovery times, lessened morbidity, and cost savings. For example, novel tools and visualization techniques are being used to perform the same surgery through smaller incisions decreasing the recovery times and risks for patients. Other MIS methods, such as the present invention described herein, attempt to achieve the same result through an entirely new approach.
A variety of different surgical techniques, including laminotomy, laminectomy, and laminoplasty, have been reported for treatment of spinal stenosis. These techniques all rely on either visualization of the anatomical structures either directly or with the use of visual and imaging aids such as cameras, or fluoroscopic or plain X-ray assisted techniques. These procedures are performed using techniques that “rongeur” (French verb to nibble or piece-wise remove) the lamina to remove or reshape it. Other techniques describe burring or scraping of the bone. These methods, however, are all performed by removing the bone from the anterior-posterior axis of the lamina 9, perpendicular to the longitudinal axis of the lamina 8 (see FIGS. 1A and 2A).
In U.S. Pat. No. 6,358,254, Anderson discloses a method for performing spinal surgery in the lumbar vertebrae to alleviate spinal stenosis, wherein the vertebra is cut at the pedicle in at least one location, the portion of the cut vertebra posterior to the facet joint is separated from the vertebral body to expand the spinal canal, and the separated portion is secured to the vertebral body by mechanical means to allow the vertebra to heal. In U.S. Pat. No. 7,166,107 and U.S. application Ser. No. 11/656,790 (published as 20070219555), Anderson discloses a method for expanding the lumbar spinal canal by drilling a passage into a lumbar vertebra and inserting a side-cutting instrument to make the pedicle cut from within the drill hole. The separated portion is again secured to the vertebral body by mechanical means to allow healing as well as to allow the secured vertebral structure to regain its load-bearing function.
Known techniques and instruments, however, do not provide a method to ensure accurate and safe dividing of the lamina while minimizing the risk of damaging any neuronal elements. In particular, the methods described by Anderson are only suitable for use in the lumbar spine, where there is little or no risk of damage to the spinal cord or vertebral artery as is the case in the cervical or thoracic spine
In view of the above, one aspect of the present invention relates to a method and device to divide the lamina in the sagittal or oblique sagittal plane 8, directed in the approximate longitudinal axis of the lamina, with the dividing instrument directed either toward the head (cephalad) or toward the tailbone (caudate). This method of dividing the lamina has not heretofore been described in open or image guided methodology. To perform this method of dividing the lamina, one aspect of the invention involves a novel guard that is inserted through the inter laminar space protecting the para-laminar structures including the neuronal elements. The guard acts to precisely guide the division of the bone while minimizing risk of injury to the neuronal elements. Furthermore, the division, cutting, drilling, burring or other techniques for removing or dividing bone compressing the neuronal elements can be done under CT scan, X-ray, fluoroscopy, MRI, or other image guidance technology to guide the division. Additionally, a surgically implantable device designed to prevent anterior translation of the divided posterior elements by means of increasing the width of the divided posterior laminar segment or decreasing the width of the divided laminar segment overlaying the central canal is disclosed (see FIGS. 7A, 7B, and 9).